This disclosure relates to passive radiators and related devices (e.g., loudspeakers).
Passive radiators (sometimes referred to as “drones” or “drone cones”) are acoustic elements that can be used to increase the low frequency output of a loudspeaker, thereby giving the loudspeaker comparable performance characteristics to those of a larger system. A passive radiator typically has the appearance of a standard cone type electro-acoustic transducer, but with the electric motor (coil and magnet) removed; and generally includes a diaphragm, and a suspension (a/k/a “surround”), and, in some cases, a mounting frame.
In typical use, a passive radiator is mounted to an acoustic enclosure (a sealed speaker box) along with an electro-acoustic transducer (a/k/a/“speaker” or “driver”) that converts electrical signals to acoustic energy. The sound pressure resulting from the acoustic energy provided by the electro-acoustic transducer drives the motion of the passive radiator. The movement of the passive radiator creates sound waves just as a normal transducer does.
Often, a passive radiator is tuned to change the way its compliance interacts with the motion of air in the acoustic enclosure by adding a mass to its diaphragm. In some cases, the mass (e.g., a metal block) is secured to the diaphragm with an adhesive.
In some alternative configurations the surround is molded directly around the mass in an insert molding process, or a multi-shot injection molding process. Such assembly processes effectively render the mass inseparable, and, thus, may not be ideal where tuning adjustments are desirable.